Descriptions

When Douglas-fir and red alder grow in mixture, interactions between the two species can be competitive, facilitative, or a combination of both over time. A number of factors have recently led to increased interest in managing these two species together for commercial production, and ongoing investigations are yielding important information about how interactions between the two species affect stand structure and productivity. Many wood quality attributes are ultimately controlled by physiological processes, which in turn are affected by competition within a forest stand. This research addressed how stand structure in young, mixed red alder/Douglas-fir plantations was associated with variations in growth form and wood quality. Branch attributes and cambial growth patterns in Douglas-fir and stem form
attributes in red alder were analyzed as a function of species proportion and timing of establishment in 15-year-old mixed plantations in the Oregon coast range. When
the two species were planted simultaneously, only mixed stands with low (10% of total stand density) proportions of red alder had low Douglas-fir mortality. In these stands, red alder stem form was poor, with a high incidence of multiple stems, low live crown bases, and considerable stem lean and sweep. Douglas-fir trees had a relatively short season of cambial growth and many were highly suppressed. When red alder planting was delayed five years, Douglas-fir trees had a short cambial growth season when the proportion of red alder in the stand was high
(75%). Douglas-fir crown base height was low when the proportion of red alder was high, but branch sizes were relatively consistent across species proportions. Percent latewood in Douglas-fir was not affected by species proportion. Red alder stem form was consistent across all levels of species proportion. It is suggested that the differences observed are a result of differential juvenile growth rates of the two species and subsequent different levels of light availability to individual tree crowns through stand age 15. Simultaneous planting of the two species at these spacings results in either unacceptable Douglas-fir growth and mortality rates or poor red alder stem form, depending on species proportion. Delayed planting of red alder appears to improve red alder stem form
and results in acceptable Douglas-fir wood quality attributes, if red alder proportion
is 50% or less. Because these stands are not yet of harvestable size, further monitoring is needed to assess how the patterns of growth and wood quality described would affect eventual product recovery.